This invention relates to wall slabs and more particularly to wall slabs formed of concrete and suitable for use in creating concrete building structures.
Extensive efforts have been directed toward developing construction blocks of foam plastic having central voids adapted to receive concrete slurry. The blocks act as forms for molding the load supporting reinforced concrete frames and remain in place to provide the finished wall surfaces, insulation and vapor barrier. The foam plastic does not act as a load bearing member in the finished structure but simply acts to retain the concrete slurry in the form during the hardening or curing process. The lightweight of the plastic allows these blocks to be made in relatively large modules, and yet be handled manually without any special material handling equipment. The blocks are typically formed with interlocking configurations on their edges so that a plurality of blocks may be stacked relative to one another with their voids aligned to form continuous channels for the reception of the concrete slurry.
It has been proposed that these blocks be formed of polyurethane, polystyrene or other foam plastic materials. One obstacle to the widespread use of these blocks in construction has been the fact that all of these organic materials decompose to varying extents under sufficient heat, sometimes generating noxious gases. Some may additionally tend to support combustion to a degree.
Certain forms of porous inorganic materials exist such as stranded fiberglass which do not decompose to any appreciable extent under heat nor support combustion and it has been proposed that the lightweight block forms for reinforced concrete construction be formed of these materials. Blocks formed primarily of these inorganic materials do improve the fire resistance of a structure relative to the resistance of a structure formed of foam plastic blocks, but they create several new problems.
Specifically, these inorganic materials have substantially higher thermal conductivity than the foam plastic materials and accordingly the resultant structures are not nearly as well insulated per relative unit thickness of material. Further, inorganic foam materials in general, and those based on glass in particular, are very expensive and very brittle and may easily break in transit or when subjected to the forces created during vibration of the concrete slurry. Additionally the inorganic forms are not self-foaming, are much more difficult and expensive to mold than the foam plastics, and are much heavier as well.
It has also been proposed to form these blocks on a composite basis with a central core of a foam plastic sheathed on its four sides by inorganic foam material so that the organically based plastic foam is completely encased within the inorganic foam. Whereas these composite blocks eliminate the noxious foam problem of the foam plastic and improve the thermal conductivity properties of the block, they still retain the relatively brittle and easily breakable material at the outer surfaces of the block; the block is relatively expensive and complicated to manufacture; and the block is relatively difficult to handle.
It has also been proposed to fabricate these blocks from tubes and sheet metal structures as shown, for example, in U.S. Pat. No. 4,098,042. These fabricated blocks are quite expensive, however, and their load bearing capacity is quite limited.